A complex Tibetan upper mantle: A fragmented Indian slab and no south-verging subduction of Eurasian lithosphere

Due to the non-uniform seismic station coverage in Tibet, critically important questions remain about the existence of southward continental subduction of Eurasia beneath northern Tibet from north, and the nature of the underthrusting Indian lithosphere underneath southern Tibet from south. Using differential P- and S-wave travel-times measured from 301 stations of all the temporary experiments deployed throughout Tibet, we constructed a comprehensive tomographic model. The upper mantle of northern Tibet consists of a rather homogeneous low velocity zone with no evidence of southward Asian continental subduction. In contrast the upper mantle from the Himalayas to central Tibet exhibits laterally variable P- and S-wave velocities. Significant low velocity zones are observed that are elongated in a north-south direction and extending to at least 150. km depth, which we interpret as evidences for fragmentation of the underthrusting Indian continental lithosphere.